package com.itcv.leetcode.low;

public class LinkedListMerge {
    public static void main(String[] args) {
        LinkedListMerge merge = new LinkedListMerge();
        ListNode l1 = merge.addListNode1();
        ListNode l2 = merge.addListNode2();

        merge.mergeTwoLists(l1,l2);

    }

    public ListNode addListNode1(){

        ListNode l1 = new ListNode(1);
        ListNode n1 = new ListNode(2);
        l1.next = n1;
        ListNode n2 = new ListNode(3);
        n1.next = n2;
        return l1;
    }

    public ListNode addListNode2(){
        ListNode l2 = new ListNode(1);
        l2.next = new ListNode(3);

        return l2;
    }

    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode prehead = new ListNode(-1);

        ListNode prev = prehead;
        while (l1 != null && l2 != null) {
            if (l1.val <= l2.val) {
                prev.next = l1;
                l1 = l1.next;
            } else {
                prev.next = l2;
                l2 = l2.next;
            }
            prev = prev.next;
        }

        // 合并后 l1 和 l2 最多只有一个还未被合并完，我们直接将链表末尾指向未合并完的链表即可
        prev.next = l1 == null ? l2 : l1;

        return prehead.next;


    }

     class ListNode {
      int val;
      ListNode next;
      ListNode() {}
      ListNode(int val) { this.val = val; }
      ListNode(int val, ListNode next) { this.val = val; this.next = next; }
  }
}
